The present invention relates to structure for connecting tubular member to fuel tank, such as hose connecting pipe or valve-housing, for example, for connecting to a fuel tank of an automobile.
FIG. 8 shows an example of a prior art fuel tank system which is installed in an automobile so that gasoline is fed to an engine. In this instance, gasoline is supplied in a fuel tank A through a filler hose B and a connecting pipe C, by means of a fueling gun (not shown) inserted into a filler pipe D connected to a filler hose B. Gasoline in the fuel tank A is fed to an engine by a fuel pump E through a feed hose F, and excess gasoline is collected through a return hose G into the fuel tank A. A communication pipe D-1 is branched from the upper portion of the filler pipe D, and a communication hose H, which is connected to the communication pipe D-1, is attached at the tip end portion thereof via a connecting pipe I to the fuel tank A. The tip end portion of the connecting pipe I extends into the fuel tank A, or stays in the fuel tank A in such a manner as to reach gasoline surface or liquid level therein when the fuel tank A is full-filled state. The fueling gun is equipped with a mechanism (not shown) which stops fueling automatically, when sensing that the tip end portion of the connecting pipe I stays under the surface of the gasoline (dips in gasoline) in the fuel tank A, that is, the tank A is full-filled state. And, an evaporative emission hose J is connected via roll over valves K, K to the fuel tank A at the upper portion thereof. Evaporated gasoline or gasoline vapor filled in the fuel tank A flows through the evaporative emission hose J to a canister. The roll over valves K, K are closed on occasion of an automobile rolling over, and the like, so as to prevent gasoline or fuel from flowing into the evaporative emission hose J.
Meanwhile, usually, a fuel tank A is made of thermoplastic resin material, due to reason that it is light weight, does not rust and is easily formed into designated shape, and so on. For example, a fuel tank A has a multi-layer composition, a layer or layers of high density polyethylene(HDPE), at least for an outermost layer, and an internal fuel barrier layer or layers such as polyamide(PA, nylon), or ethylene vinyl alcohol(EVOH) which are bonded or fused to the HDPE layer or layers respectively by a bonding layer or bonding material. HDPE is often applied also for a connecting pipe C to connect a filler hose B to a fuel tank A and a housing of roll over valve K In prior connecting structure shown in FIG. 9, a connecting pipe C is formed into a relatively elongated tubular member made of HDPE, with which a flange C-1 for fusing is integrally formed at the axial center thereof and in the inner peripheral surface of the connecting pipe C, a metallic cylindrical body L extending from the upper end to below the axial center of the connecting pipe C is provided. The connecting pipe C thus configured is inserted into an opening M of the fuel tank A, comprising an outer layer N made of HDPE, an inner layer O made of HDPE and a fuel barrier layer P made of PA therebetween, and fixed onto the fuel tank A(outer layer N made of HDPE) by fusing the flange C-1 of the connecting pipe C thereto.
In some cases, the connecting pipe C itself is made of thermoplastic resin having good gasoline permeability resistance such as PA, and the connecting pipe C thus configured is fused and fixed onto the fuel tank A. Usually a connecting pipe C made of PA cannot be directly fused onto a fuel tank A made of HDPE. However, Japanese Patent No.2715870 and German Patent No. 19535413(DE19535413C1) disclose inventions relating to fixing a PA tubular member onto an opening of the HDPE fuel tank by means of bonding member or bonding material(bonding member layer). And, a prior art technology shown in FIG. 10 is actually applied for connecting a connecting pipe to a fuel tank. In connecting structure with application of bonding materials for fusing shown in FIG. 10, a bonding member layer Q of modified polyethylene (modified PE) compatible with PA, is beforehand bonded or fused onto the back surface of a flange C-2 of the PA connecting pipe C, and is fused onto the surface of the rim portion of the opening M(surface layer or outer layer N of HDPE) provided on the fuel tank A when connecting pipe C the connecting to the fuel tank A, so that the connecting pipe C is fixed onto the fuel tank A.
However, in the connecting structure shown in FIG. 9, evaporated gasoline or gasoline might penetrate in a clearance created between the outer surface of the connecting pipe C and the rim or the inner peripheral surface of the opening M, and might permeate through the HDPE flange C-1 having insufficient gasoline permeability resistance (refer to arrows in FIG. 9), resulting in permitting evaporated gasoline (vapor fuel) to diffuse or flow out into the air. And, even in the connecting structure shown in FIG. 10, since modified PE used for a bonding member layer Q is usually inferior to HDPE used for the fuel tank A in gasoline permeability resistance, evaporated gasoline could permeate through the bonding member layer Q and diffuses out into the air (refer to arrows in FIG. 10).